Primary side constant output current controller

ABSTRACT

A lower-cost and more precise control methodology of regulating the output current of a Flyback converter from the primary side is provided. The methodology regulates the output current accurately in both continuous current mode (CCM) and discontinuous mode (DCM) and can be applied to most small, medium, and high power applications such as cell phone chargers, power management in desktop computers and networking equipment, and, generally, to a wide spectrum of power management applications. Two highly integrated semiconductor chips based on this control methodology are also described that require very few components to build a constant current Flyback converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present utility patent application claims priority benefit of theU.S. provisional application for patent having Ser. No. 60/691,980,filed on Jun. 16, 2005, under 35 U.S.C. 119(e). The contents of thisrelated provisional application are incorporated herein by reference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor patent disclosure as it appears in the Patent and Trademark Office,patent file or records, but otherwise reserves all copyright rightswhatsoever.

FIELD OF THE INVENTION

The present invention relates generally to the field of powerconversion. More particularly, the invention relates to switching modepower supplies with regulated output current.

BACKGROUND OF THE INVENTION

With the aggressive growth of battery powered portable electronics,e.g., cell phones, the demand for lower cost, lighter weight and betterefficiency battery chargers is very high. Historically, linear powersupplies have been employed. However, despite being low in cost, theycannot generally outperform switching mode power supplies, which havelower weight and much higher efficiency. For many applications, theFlyback converter is often chosen from among different switching modetopologies to meet this demand due to its simplicity and goodefficiency.

Over the years, various integrated circuit (IC) chips have beendeveloped and used to build constant current Flyback power supplies. Forexample, FIG. 1 is an illustration of a prior art secondary sidecontrolled constant output current Flyback converter. Such a convertercomprises a transformer 201 (which has three windings), a secondary sideresistor 301 (which represents the copper loss of transformer 201), aprimary switch 105, a current sense resistor 106, a secondary rectifier302, an output capacitor 303, an optical coupler 202, a second currentsense resistor 305, a bias resistor 304, a current limit transistor 306,and a conventional Pulse Width Modulation (PWM) control IC 104. Resistor101 and capacitor 102 provide the initial start-up energy for IC 104. Ageneral characterization of basic concepts of operation will bedescribed next. Once the Flyback converter is stable, IC 104 is poweredby the auxiliary winding (with Na number of turns) of transformer 201via rectifier 103. The output current is controlled by resistor 305 andtransistor 306. Transistor 306 regulates the voltage across resistor 305to a preset voltage VBE (e.g., 0.65V). The output current, therefore, isequal to VBE divided by the resistance of resistor 305. This circuit,however, is generally undesirable at least both because VBE and theoutput current vary with temperature and the voltage VBE causessignificant power loss.

Some known approaches for primary feedback control of constant outputcurrent switching regulators teach the use of a reflected auxiliarywinding voltage or current to control the primary inductor peak current.One known deficiency of such known methods is that the output currentconstant control is applicable only in discontinuous conduction mode(DCM) operation, thereby limiting the power capability of the powerconverter. For operation in continuous conduction mode (CCM), currentindustry solutions almost entirely rely exclusively on the use of anoptocoupler as shown in FIG. 1. Typically, they will use the auxiliarycurrent/voltage (e.g., via diode and RC filters) to control the peakprimary current. When auxiliary current (i.e., the control current)decreases, the primary current is reduced. Some known techniques useauxiliary voltage to control primary current by essentially scaling thepeak current (IPEAK) as proportional to a square root of the outputvoltage; i.e., SQRT(VOUT).

In view of the foregoing, what is needed is a relatively low-cost andeffective control methodology of regulating the primary side outputcurrent of a Flyback converter. It would be desirable if at least someof the foregoing limitations of the prior art are overcome for operationin both continuous current mode (CCM) and discontinuous mode (DCM),preferably with a minimal number of IC chips (e.g., two IC chips). It isfurther desirable that the need for a secondary circuit and opticalcoupler are eliminated, and that the output current of a Flybackconverter be largely insensitive to temperature variations.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is an illustration of a prior art secondary side controlledconstant output current Flyback converter;

FIG. 2 is an example of a primary side controlled constant outputcurrent Flyback converter according to a first embodiment of the presentinvention;

FIG. 3 illustrates an exemplary block diagram of IC chip shown in FIG. 2in accordance with an embodiment of the present invention;

FIG. 4 illustrates exemplary ideal waveforms of the auxiliary windingvoltage, primary switch current, and secondary rectifier currentoperating in continuous current mode (CCM) according to an embodiment ofthe present invention;

FIG. 5 illustrates exemplary ideal waveforms of the auxiliary windingvoltage, primary switch current and secondary rectifier currentoperating in discontinuous current mode (DCM) according to an embodimentof the present invention;

FIG. 6 illustrates an exemplary schematic of a primary side controlledconstant output current Flyback converter in an Emitter Switchingconfiguration using the first IC chip embodiment, in accordance with anembodiment of the present invention;

FIG. 7 illustrates an exemplary block diagram of a PWM controller ICchip 704, in accordance with a second embodiment of the presentinvention;

FIG. 8 is an exemplary schematic of a primary side controlled constantoutput current Flyback converter using the second embodiment with anexternal MOSFET and current sensing resistor;

FIG. 9 illustrates a schematic diagram of an exemplary digital frequencyjittering circuit that is suitable to implement the foregoing jitterfunctional block, in accordance with an embodiment of the presentinvention; and

FIG. 10 illustrates an exemplary jitter frequency control logic diagramfor the exemplary digital frequency jittering circuit of FIG. 9, inaccordance with an embodiment of the present invention

Unless otherwise indicated illustrations in the figures are notnecessarily drawn to scale.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects and in accordance with thepurpose of the invention, a variety of techniques to regulate the outputcurrent of a switching regulator are described.

Some embodiments of the present invention provide a primary side,constant output current PWM controller system and/or IC for a switchingregulator with a transformer having at least a primary, a secondary, andan auxiliary winding, where the system or regulator includes: areference signal for setting the output current level of the switchingregulator; a transformer reset time detector that has a feedback inputfor the auxiliary winding of the transformer used in a switchingregulator and computes a transformer reset time signal based on theauxiliary winding feedback input; a multiplier, which outputs acalculation (e.g., multiplication) on signals that is derived from afeedback signal corresponding to the output current of the switchingregulator and the transformer reset time signal, the output of themultiplier being operable as a calculated output current; an erroramplifier, which outputs a signal based on the difference between thereference signal and the calculated output current; a comparator that isconfigured to compare one or more ramp signals such as, withoutlimitation, the output of the calculator unit, the error amplifieroutput and/or the output current feedback signal; a PWM controllermodule that outputs a PWM switching regulator control signal based on anoscillator output and the comparator output; and a gate drive modulethat receives the PWM control signal and generates a corresponding gatedrive signal operable for properly turning on and off a switched poweroutput device of the switching regulator.

A multiplicity of other embodiments may further provide variations ofthe prior embodiments in which the reference signal is a programmablecurrent mirror circuit operable to output a programmed current; and/orin which the switched power output device is a power MOSFET that isconfigured as the main power switch of the switching regulator; and/orembodiments further include a current sensing circuit for generating theoutput current feedback signal where the current sensing circuitoptionally comprises a MOSFET connected in parallel with the switchedpower output device; and/or in which the comparator is a peak currentmode PWM comparator with a slope-compensation input.

Another embodiment of the present invention provides means for achievingthe functions described in the foregoing system embodiments.

In yet other embodiments of the present invention, a constant outputcurrent PWM controller printed circuit board (PCB) module is describedthat includes a PCB and an embodiment of the foregoing integratedcircuit device joined onto the PCB, where the PCB can be optionallypopulated with the necessary electronic components such that, infunctional combination with the integrated circuit (IC) device, the PCBmodule is operable to perform as a constant current switching regulator.

A method, according to another embodiment of the present invention, isprovided for regulating the output current of a Flyback converter fromthe primary side, and such method includes steps for: computing acalculated output current based on the average current of a primarypower switch and a transformer reset time, regulating the output currentof the Flyback converter to a desired value, and reducing thetemperature sensitivity of the output current.

Other features, advantages, and object of the present invention willbecome more apparent and be more readily understood from the followingdetailed description, which should be read in conjunction with theaccompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is best understood by reference to the detailedfigures and description set forth herein.

Embodiments of the invention are discussed below with reference to thefigures. However, those skilled in the art will readily appreciate thatthe detailed description given herein with respect to these figures isfor explanatory purposes as the invention extends beyond these limitedembodiments. For example, it should be appreciated that those skilled inthe art will, in light of the teachings of the present invention,recognized a multiplicity of alternate and suitable approaches,depending upon the needs of the particular application, to implement thefunctionality of any given detail described herein, beyond theparticular implementation choices in the following embodiments describedand shown. That is, there are numerous modifications and variations ofthe invention that are too numerous to be listed but that all fit withinthe scope of the invention. Also, singular words should be read asplural and vice versa and masculine as feminine and vice versa, whereappropriate, and alternatives embodiments do not necessarily imply thatthe two are mutually exclusive.

The present invention will now be described in detail with reference toembodiments thereof as illustrated in the accompanying drawings.

FIG. 2 illustrates an exemplary circuit implementing a PWM controller ICchip 204, in accordance with a first embodiment of the presentinvention. The circuit shown is a primary side controlled constantoutput current Flyback converter. The converter shown comprises atransformer 201 (which has three separate coil windings: primary withN_(p) turns, secondary with N_(s) turns, and auxiliary with N_(a)turns), a secondary side resistor 301 (which represents the copper lossof transformer 201), a secondary rectifier 302, an output capacitor 303,and a peak current mode PWM control IC 204. Resistor 101 and capacitor102 provide the initial start-up energy for IC 204. Once the Flybackconverter is stable, IC 204 is powered by the auxiliary winding oftransformer 201 via rectifier 103. Resistor 109 programs the outputcurrent. Resistor dividers 105 and 106 then provide an input signal forcomputing the transformer reset time (T_(r)) via the T_(r) Detectioncircuit inside IC 204.

FIG. 3 illustrates an exemplary block diagram of IC chip 204 shown inFIG. 2 in accordance with an embodiment of the present invention. Asillustrated, V_(CC) supply 401 provides an internal power supply andreference voltage. Current mirror 402 duplicates current I_(set) toresistor 403. T_(r) Detection 405 computes T_(r) based on the V_(a)voltage waveform coming from FB input pin. Those skilled in the art, inlight of the teachings of the present invention, will readily recognizethat the feedback for the FB input pin may come from any other suitablesource beyond the auxiliary winding of the transformer such as, by wayof example, and not limitation, from the primary winding. In alternateembodiments of the present invention (not shown), the transformer doesnot have any auxiliary windings, and only has a primary and a secondarywinding. Those skilled in the art, will recognize a multiplicity ofalternate and suitable transformer types and interface circuitconfigurations to be operable with connection to the FB input pin.

In the embodiment shown, calculation unit 406 performs multiplicationbetween I_(P) _(—) _(AVG) and T_(r), however, in other embodiments ofthe present invention, depending on the needs of the particularapplication, any suitable math function may be implemented instead ofmultiplication, as will be readily determined by those skilled in theart, in light of the present teachings.

Error amplifier 404 then compares the calculated output current with aprogrammed value across resistor 403. Resistor 407 and capacitor 408 arecoupled to form an averaging circuit for the primary current. Resistor409 and capacitor 410 form a compensation network for amplifier 404.Comparator 412 serves as a peak current mode PWM comparator with anoptional slope compensation input. In other embodiments of the presentinvention (not shown), the comparator may be configured by those skilledin the art to compare any suitable ramp signals depending upon the needsof the particular application. System oscillator 411 provides anoptional frequency jittering function that widens the frequency spectrumand achieves a lower conducting EMI emission. An example of a preferredfrequency jittering circuit is described in connection with FIG. 9.

Alternate embodiments of the present invention may not include thefrequency jittering function in system oscillator 411 and/or slopecompensation. In many applications, slope compensation and the systemoscillator jitter function can improve converter operation in certaininput/output operating conditions; however, these functions arecompletely optional, whereby alternate embodiments of the presentinvention may not include either one or both.

PWM control unit 417 then generates the correct PWM waveform byutilizing a cycle-by-cycle current limiting function. MOSFET 413 is arelatively high speed MOSFET gate driver. Power internal MOSFET 415serves as the main switch, while a small die size allocated internalMOSFET 414 and resistor 416 form a current sense circuit. As will bereadily apparent to the system designer, some applications may notrequire resistor 416 to generate the current sensing voltage feedback orit may be located in other circuit configurations, or embedded intoother system components. As will be readily recognized by those skilledin the art, depending upon the needs of the particular application andcurrent technology, the power MOSFET may be formed in any suitablemanner. By way of example, and not limitation, the power MOSFET may becomprised of a multiplicity of smaller MOSFET device to form a singlepower MOSFET. In contrast with conventional approaches that only work inDCM, the present embodiment implements a method for using “sampledAuxiliary Flyback Voltage” to control the primary current. Sampling theAuxiliary Flyback Voltage at a known time point provides a more accuraterepresentation of the actual output voltage in most applications. Thepresent embodiment is largely independent of auxiliary voltage and/orcurrent by, for example, basing output current control only on primarycurrent sensing and the ratio of T_R/T_ON, which works in both DCM andCCM. Hence, embodiments of the present invention preferably do not useauxiliary voltage to control primary current by essentially scaling thepeak current (IPEAK) as proportional to a square root of the outputvoltage, as is done in conventional approaches.

FIG. 4 illustrates exemplary ideal waveforms of the auxiliary windingvoltage, primary switch current, and secondary rectifier currentoperating in continuous current mode (CCM) according to an embodiment ofthe present invention. Main switch 415 turns on at t₁, turns off at t₂and turns on again at t₃. The switching period is T, the turn-on time isT_(on) and the turn-off time is T_(r). Using known theory, the outputcurrent I_(out) can be expressed as:I _(out)=(½)·(I _(S1) +I _(S2))·(T _(r) /T).  (1)BecauseI _(S1)=(N _(P) /N _(S))·I _(P1)  (2)andI _(S2)=(N _(P) /N _(S))·I _(P2),  (3)I_(out) may be expressed by combining (1), (2) and (3) as shown in (4)below.I _(out)=(½)·(N _(P) /N _(S))·(I _(P1) +I _(P2))·(T _(r) /T).  (4)Furthermore, becauseI _(P) _(—) _(AVG)=(½)·(I _(P1) +I _(P2))·(T _(ON) /T)  (5)equations (4) and (5) may be combined to express I_(out) as shown in (6)belowI _(out)=(N _(P) /N _(S))·(T _(r) /T _(ON))·I _(P) _(—) _(AVG)  (6)

FIG. 5 illustrates ideal waveforms of the auxiliary winding voltage,primary switch current, and secondary rectifier current operating indiscontinuous current mode (DCM) according to an embodiment of thepresent invention. Main switch 415 turns on at t₁, turns off at t₂, andturns on again at t₄. The switching period is T, the turn-on time isT_(on) and the turn-off time is equal to (t₄-t₂). As shown in FIG. 5,the current at the secondary winding of transformer 201 discharges tozero at t₃. Because Tr is equal to (t₃-t₂), the output current can beexpressed as:I _(out)=(½)·I _(S2)·(T _(r) /T).  (7)Because I _(S2)=(N _(P) /N _(S))·I _(P2),(8)I_(out) may be expressed by combining (7) and (8) as shown in (9) below:I _(out)=(½)·(N _(P) /N _(S))·I _(P2)·(T _(r) /T).  (9)Furthermore, becauseI _(P) _(—) _(AVG)=(½)·I _(P2)·(T _(ON) /T),  (10)

I_(out) may be expressed by combining (9) and (10) as shown in (11)belowI _(out)=(N _(P) /N _(S))·(T _(r) /T _(ON))·I_(P) _(—) _(AVG)  (11)

The output power of the converter generally depends only on the storedenergy of the inductor in DCM operating mode, in accordance with thefollowing formula (12), which neglects efficiency losses:Vo*Io=(½)*Lp*Ip ² *F.  (12)In the CCM operating mode, at the output of the converter output, thevoltage is dropping from V_(norm) to zero. To keep Io constant, F ispreferably reduced proportionally to Vo while maintaining a fixed Ip.

FIG. 6 illustrates an exemplary schematic of a primary side controlledconstant output current Flyback converter in an emitter switchingconfiguration using the first IC chip embodiment, in accordance with anembodiment of the present invention. For many low power applications,using current on-chip MOSFET technology, no external power MOSFET orcurrent sense circuit is needed. For higher output power and/or higherswitching frequency than the internal on-chip MOSFET can properlyhandle, however, external power handling components may be required. Forexample, the approach of the present embodiment is to introduce NPNbipolar transistor 105 that cooperates with IC chip 204, of the presentinvention, in an emitter switching configuration as shown in the figure.In such a configuration, internal MOSFET 415 drives the emitter ofexternal NPN transistor 105 which serves as the main switch. To furtherincrease the power handling capability and switching frequency, anexternal MOSFET is typically used as the main switch.

FIG. 7 illustrates an exemplary block diagram of a PWM controller ICchip 704, in accordance with a second embodiment of the presentinvention. IC chip 704 does not include internal power MOSFET 415,current sensing MOSFET 414, and current sensing resistor 416 from thefirst IC chip embodiment of FIG. 3. In this second embodiment, thecurrent driving capability of gate drive 413 results in improved controlfor larger MOSFETs. FIG. 8 illustrates an exemplary schematic forimplementing IC chip 704 with an external MOSFET and a current senseresistor.

The functional blocks shown in the prior embodiments may be implementedin accordance with known techniques as will be readily apparent to thoseskilled in the art. However, some embodiments of the present inventioninclude implementation approaches that are not conventional. Forexample, without limitation, the foregoing jitter functional block maybe implemented as follows. FIG. 9 illustrates a schematic diagram of anexemplary system oscillator 411 having a digital frequency jitteringcircuit that is suitable to implement the foregoing jitter functionalblock, in accordance with an embodiment of the present invention. Thefrequency jittering in the present embodiment is implemented by adigital control scheme, which departs from known approaches. Anoscillator 817 is preferably a current controlled oscillator. There ispreferably an uncontrolled, base-line, current source 801, which, in oneaspect, is present to set a minimum oscillator frequency, Fmin, that theswitched current sources will jitter from. In the embodiment shown, thecurrent to oscillator 817 is controlled by a multiplicity of switchedcurrent sources 802-804 that carry out the jittering of the oscillator'sminimum frequency. The frequency of the system oscillator output signalis generally proportional to the total current entering into oscillator817. In alternate embodiments, any number of current sources may beimplemented depending upon the needs of the particular application. Thejitter behavior is generated by feeding back the output signal ofoscillator 817 to a multiplicity of series connected flip-flops (e.g.,818 to 823). Current sources 801, 802, 803 and 804 are presentlypreferred to be currents of magnitudes 100 μA, 2.5 μA, 5 μA and 10 μA,respectively. Each switched current source is presently configured withfour current control switches (e.g., control switches 805, 806, 811 and812 for switched current source 802) that are arranged in two parallellegs with each leg having two switches in series. In this way, forcurrent to flow into oscillator 817 at least one leg must have both ofits switches turned on. In similar fashion, four switches (807, 808, 813and 814) are connected to switched current source 803 and another fourswitches (809, 810, 815 and 816) are connected to switched currentsource 804. All of these switches are closed or open by a control inputfrom an output from the series connected flip-flop chain. In the exampleshown, the switch 805 is open when Q₅ is at logic level “1” and isclosed when Q₅ is at logic level “0”. Similarly, the 806 switch is openwhen Q₅ is at logic level “0” and is closed when Q₅ is at logic level“1”, and so on. When all the switched current sources are enabled, amaximum frequency, Fmax, of the system oscillator output signal isachieved. As will be readily apparent to those skilled in the art, inlight of the present teachings, the choice of which flip-flop outputsconnect to which current control switch will determine a certainjittering pattern. An aspect of this digital frequency jittering schemeis that the period & the step of frequency variation may be relativelyprecisely controlled, and is largely insensitive to temperaturevariations. It should be appreciated that in contrast to conventionalanalog techniques for jittering the oscillator frequency, the digitaljittering approach of the present embodiment always provide digitallycalculated frequency step irrespective of the known shortcomings thatanalog based techniques suffer from; such as, without limitation,temperature, input, output age dependences, etc. Those skilled in theart, in light of the present teachings, will readily recognize amultiplicity of alternate and suitable implementations that implementthe spirit of the present embodiment. By way of example, and notlimitation, current based operation may be replaced with a voltage basedapproach, and the number and topology of the switches and/or currentsources and/or flip-flop chain may be altered as needed for theparticular application, and other suitable means to selectively controlthe pattern of current flowing into the current controlled oscillator.

FIG. 10 illustrates an exemplary jitter frequency control logic diagramfor the exemplary digital frequency jittering circuit of FIG. 9, inaccordance with an embodiment of the present invention. In the exampleshown, frequency variation from its maximum (Fmax) to minimum (Fmin)corresponding to the logic states “0” or “1” of Q₂, Q₃, Q₄ and Q₅.

Having fully described at least one embodiment of the present invention,other equivalent or alternative methods of implementing a primary sideconstant output current controller according to the present inventionwill be apparent to those skilled in the art. The invention has beendescribed above by way of illustration, and the specific embodimentsdisclosed are not intended to limit the invention to the particularforms disclosed. The invention is thus to cover all modifications,equivalents, and alternatives falling within the spirit and scope of thefollowing claims.

1. A constant output current controller system for a switching regulatorthe system comprising: a transformer reset time detector with an inputlead that is operable to receive a feedback signal derived from atransformer winding—and, wherein the transformer reset time detectorcomputes a transformer reset time signal based in part on the feedbacksignal, and wherein the transformer reset time signal represents aduration of time until the feedback signal has decayed to approximatelya steady rate; a calculator unit, that generates a combined signal bymultiplying the transformer reset time signal by a current signalthrough a power switch; an error amplifier, which outputs a signal basedon the difference between a reference signal and the combined signal,wherein the reference signal is sets by an output current level of theswitching regulator; a comparator that is configured to compare thecombined signal and at least one ramp signal; an oscillator, wherein theoscillator output includes jitter generated signal digitally as opposedto using an analog technique; a PWM controller module that outputs a PWMswitching regulator control signal based on an oscillator output fromthe oscillator and an output from the comparator; and a gate drivemodule that receives the PWM switching regulator control signal andgenerates a corresponding gate drive signal operable for properlyturning on or off the power switch of the switching regulator, whereinthe gate drive signal turns the power switch on and off such that theoutput current level of the switching regulator remains constant.
 2. Theconstant current controller system of claim 1, further comprising: aprogrammable current mirror circuit, wherein the programmable currentmirror circuit outputs the reference signal.
 3. The constant currentcontroller system of claim 1, wherein the power switch comprises a powerMOSFET that is configured as a main power switch of the switchingregulator.
 4. The constant current controller system of claim 1, furthercomprising: a current sensing circuit for generating at least one of theat least one ramp signal.
 5. The constant current controller system ofclaim 4, wherein the current sensing circuit comprises a MOSFETconnected in parallel with the power switch.
 6. The constant currentcontroller system of claim 1, wherein the comparator comprises a peakcurrent mode PWM comparator with a slope-compensation input.
 7. Theconstant current controller system of claim 1, wherein the feedbacksignal is not derived from a signal associated with a secondary outputwinding of a transformer.
 8. The constant current controller system ofclaim 1, wherein the feedback signal is derived only from a signalassociated with an auxiliary winding of a transformer.
 9. The constantcurrent controller system of claim 1, wherein the power switch isconfigured to form a Flyback converter, the power switch being a powerMOSFET device or an NPN bipolar transistor in an emitter switchingconfiguration.
 10. A constant output current controller integratedcircuit (IC) device, the IC device comprising: a transformer reset timedetector, with an input lead that is operable to receive a feedbacksignal derived from a transformer winding, wherein the transformer resettime detector computes a transformer reset time signal based on thefeedback signal, and wherein the transformer reset time signalrepresents a duration of time until the feedback signal has decayed toapproximately a steady rate; a calculator circuit, that generates acombined signal by multiplying the transformer reset time signal by acurrent signal through a power switch; an error amplifier, which outputsa signal based on the difference between a reference signal and thecombined signal, wherein the reference signal is set by an outputcurrent level of the switching regulator; a comparator that isconfigured to compare the combined signal and at least one ramp signal;a gate drive module that receives a PWM switching regulator controlsignal that is based on an output of the comparator, wherein the gatedrive module generates a corresponding gate drive signal operable forproperly turning on or off the power switch of the switching regulator,wherein the gate drive signal turns the power switch on and off suchthat the output current level of the switching regulator remainsconstant; and an oscillator that generates the oscillator signal toinclude jitter generated signal digitally as opposed to using an analogtechnique.
 11. The constant current controller IC device of claim 10,further comprising: a programmable current mirror circuit, wherein theprogrammable current mirror circuit outputs the reference signal. 12.The constant current controller IC device of claim 10, wherein the powerswitch is a power MOSFET that is configured as a main power switch ofthe switching regulator.
 13. The constant current controller IC deviceof claim 10, further comprising: a current sensing circuit forgenerating at least one of the at least one ramp signal.
 14. Theconstant current controller IC device of claim 13, wherein the currentsensing circuit comprises a MOSFET connected in parallel with the powerswitch.
 15. The constant current controller IC device of claim 10,wherein the comparator comprises a peak current mode PWM comparator witha slope-compensation input.
 16. The constant current controller ICdevice of claim 10, wherein the feedback signal is not derived from asignal associated with a secondary output winding of a transformer. 17.The constant current controller IC device of claim 10, wherein thefeedback signal is derived only from a signal associated with anauxiliary winding of a transformer.
 18. The constant current controllerIC device of claim 10, wherein the power switch is external to the ICdevice and the gate drive module is configured to properly drive theexternal power switch, and wherein the external power switch is a powerMOSFET device or an NPN bipolar transistor in an emitter switchingconfiguration.
 19. The constant current controller IC device of claim10, further comprising: a printed circuit board (PCB), wherein theintegrated circuit (IC) device is communicatively coupled with the PCB,the PCB being optionally populated with the necessary electroniccomponents such that, in functional combination with the integratedcircuit (IC) device, the PCB is operable to perform as a constantcurrent switching regulator.
 20. A constant output current controllersystem for a switching regulator, the system comprising: a terminal forreceiving a signal that sets a desired output current level of theswitching regulator; means for computing a transformer reset timesignal, wherein the transformer reset time signal represents a durationof time until a feedback signal decays to approximately a steady rate;means for generating a calculated combined signal by multiplying thetransformer reset time signal by an average current; means forgenerating an error signal based on the difference between the signalthat sets the desired output current level and the combined signal;means for comparing the error signal and at least one ramp signal; meansfor generating an oscillator signal; means for generating a PWMswitching regulator control signal based on the oscillator signal and anoutput of the means for comparing; and means for generating a gate drivesignal operable for properly turning on or off a switched power outputdevice of the switching regulator, the gate drive signal correspondingto the PWM switching regulator control signal, wherein the switchingregulator outputs a constant output current.
 21. The constant currentcontroller system of claim 1, wherein the combined signal is a productof the transformer reset time signal and an average current through theprimary winding.
 22. The constant current controller IC device of claim10, wherein the combined signal is a product of the transformer resettime signal and an average current through the primary winding.
 23. Amethod comprising: determining a transformer reset time signal based ona feedback signal received from a transformer, wherein the transformerreset time signal is based in part on a rate of change of the feedbacksignal; multiplying the transformer reset time signal by an averagecurrent through a power switch to form a calculated current value;providing an error signal based on a difference between the calculatedcurrent value and a reference signal, wherein the reference signal isset by an output current level of a switching regulator; providing acomparison signal between the error signal and at least one ramp signal;outputting a switching regulator signal based on an oscillator signaland the comparison signal, wherein the oscillator signal includes jittergenerated digitally as opposed to using an analog technique; andgenerating a gate drive signal to turn-off or turn-on at the powerswitch, wherein the signal power switch is turned-off and turned-on suchthat the output current level of the switching regulator remainsconstant.
 24. The method of claim 23, wherein the transformer reset timesignal represents a duration of time over which the feedback signaldecays to approximately a steady rate.
 25. The method of claim 23,wherein the transformer reset time signal is based on a voltage waveformat an auxiliary side of the transformer.
 26. The method of claim 23,further comprising: providing a current of the power switch using acurrent sense circuit.